Which 8x4 sheet for loft stairs he area?

[Ian H]

Daughters loft storage area is ready for some flooring.

We can get 8x4 sheets up there so I was thinking of using 18mm shuttering ply because it’s strong and cheap.

Would there be any disadvantage of using that compared to the 18mm 8x2 sheets of the P5 chipboard?

 

[JohnD]

I'm sure ply is a better material, but as it is not T&G, have all joints and cut edges supported by a joist or strut (noggin). It will be easy to take up if you want to get at the ceiling lamp wiring or something in future.

The bigger the sheets, and the fewer joints, the more rigid it is.

if the existing joists are not very deep, you can counterbatten them, and lay extra insulation in the gap. When screwed down, this will spread the load over the joists and increase rigidity. When the ply is screwed down as well it will make a pretty good loft floor. I used decking timbers as they are pre-treated and cheap to buy near me. It may be a good precaution to use a timber preservative while you are doing this work.

Unless the existing joists are unusually deep, it will not meet BRs for a habitable room, or taking your piano and Chatwood-Milner up there.

 

[Ian H]

Thanks John, it’s just for storage and the joist are 6x2’s

 

[JohnD]

150mm insulation is not much by today's standards

You could increase it by the depth of counterbattens if you want.